It is a tasteless but ever-popular topic of pub scholarship: which tyrant was the craziest of them all? Given absolute power to wield, a state's whole budget to spend and complete freedom from any moral scruples, who made the most lurid use of it? Even a book called The Desktop Digest of Despots and Dictators has now appeared to help with the discussion, if not exactly raise its tone.

Certainly we are dealing with a crowded leaderboard. For years Caligula (AD12-41) has set the pace, most famously by making his horse a consul. The book also claims he staged a full-scale battle against the English Channel, in retaliation for the sea sinking some of his ships. Archers fired arrows into the water before ranks of infantry, led bravely by Caligula himself, began hacking at the waves with swords and spears.

Nor should we forget Ivan the Terrible (1530-84). As a child he was said to amuse himself by throwing dogs off towers, before moving on to cavalry charges in the street, locking naked people into courtyards for target practice, and impalement generally. An unhappy man, he did later regret killing his favourite son, and spent a lot of time smashing furniture and banging his head against the walls and floor.

Later, Anna of Russia (1693-1740) showed a more playful way of abusing power, forcing noblemen who displeased her to live costumed in giant nests, clucking, pretending to be hens. She also ordered her jester Prince Michael, a member of the old nobility she despised, to marry a scullery maid in a ceremony complete with a parade of animals and people with deformities.

Saddam Hussein (1937-2006), apparently, had a fragile side you might not know about. A longterm sufferer from obsessive-compulsive disorder, he was said to wash many times each day, and compel visitors to scrub themselves with antibacterial gel before coming into his presence.

Students of Idi Amin's colourful career will also enjoy tales of the Central African Republic's less-known despot Jean-Bedel Bokassa (1921-1996), who in 1977 spent a third of his country's annual budget on a single ceremony declaring himself emperor. The event featured drum majorettes, imported French horses and "four full-sized concrete replicas of the Arc de Triomphe". Rumours of a cannibal feast were widespread, but never proven.

Success in one's mad schemes is not a prerequisite of tyranny, though, and few tyrants could claim to be much crazier than James Harden-Hickey (1854-98), an American-French adventurer who declared himself James I of the south Atlantic island of Trinidade – then uninhabited – in 1893. The declaration provoked derision in the world's newspapers. Sadly, James I's reign lasted only two years before the British took the island for themselves, at which he tried to finance an invasion of Britain. This failed, and finally he killed himself in a Texas hotel room, leaving behind a suicide note and a homemade crown.